The newer engines place increased demands on the lubricants to be employed. In the past, a number of different additives have been added to lubricating oils to improve such properties as viscosity index and dispersancy. Significant reductions in cost can be made by employing a single additive that improves a number of lubricant properties. However, in attempting to improve more than a single lubricant property, care must be taken in not causing the deterioration of other properties. For example, in U.S. Pat. Nos. 3,687,905 and 3,864,268, copolymers of ethylene and propylene are first oxidized and degraded prior to an aminitation. This procedure results in the introduction of sites for future oxidative attack.
Significantly, known processes for making certain dispersants are not always applicable for the preparation of dispersants also having viscosity index-improving properties. For example, in U.S. Pat. No. 3,172,892, a relatively low molecular weight polymer (having about 50 carbon atoms) is reacted with maleic anhydride and an ethylene amine to form a dispersant; but, the reaction mechanism relies upon the presence of a single double bond that is inherently present at the end of the olefin polymer. When the polymer has only 50 carbon atoms, sufficient dispersancy sites may be available through the single terminal double bond. However, when the polymer has over 500 carbon atoms, such as is necessary for it to impart some viscosity index-improving properties, the single terminal double bond will not be sufficient, and a difficult derivitization means is required in order to obtain adequate dispersancy.
In addition, it is important that the polymer dispersant-VI improver have a sufficient number and type of sites with dispersant activity. Therefore, additives such as those disclosed in U.S. Pat. No. 3,454,607, prepared with mono-carboxylic acid-producing compounds may be deficient.
A new additive has been prepared that is not oxidatively degraded prior to derivitization. In addition, the preparation process for the new additive is not dependent upon the presence of double bonds in the polymer chain in order to provide reaction sites. Further, the new additive possesses good dispersancy characteristics in addition to good viscosity index-improving characteristics.